1. Field of the Invention
This invention relates to novel semiconductor devices and structures which incorporate p-type and n-type wide bandgap material formed by impurity induced layer disordering of multiple semiconductor layers. U.S. Pat. No. 5,376,583, issued Dec. 24, 1994, describes a method for making p-type doped materials alone or simultaneously with n-type disordered materials and is incorporated herein by reference.
In particular, this invention relates to five overlapping classes of novel devices: integrated transistor and edge emitting laser diodes; integrated transistors and surface emitting diodes; a laterally injected surface emitting laser diode; a carrier channeling or "nipi" device; and an interdigitated semiconductor device. Further, the laterally injected surface emitting laser diodes includes devices having active distributed optical feedback to achieve lasing oscillation. These active distributed devices may incorporate only one or both of the n-type and p-type IILD materials.
2. Related Art
Impurity-induced layer disordering of multiple layers of Group III-V compound semiconductors is an important step in fabricating optoelectronic devices such as lasers, transistors, and photodiodes. The diffusion of silicon or the like into multiple layers of Group III-V semiconductors under Group V-rich conditions is well known to form layer disordered material. Unfortunately, such impurity induced layer disordering with silicon was limited to forming n-type material. In addition, while it is known that-he diffusion of zinc into multiple layers of Group III-V semiconductors forms p-type doped layer disordered material, such p-type semiconductor materials were not suitable for use in many devices because zinc diffused materials lack an abrupt and reproducible transition from the ordered to disordered material.
Accordingly, most known devices requiring both p-type and n-type doped materials formed by impurity induced layer disordering could not be usefully manufactured.
In particular, surface emitting diode lasers are an important light source for many applications, such as optical disk systems, laser printing and scanning, optical interconnections, and fiber optic communications. One problem with such lasers is that they inherently have much less available optical gain than edge-emitting lasers, due to the small active volume of the surface emitter. Consequently, achieving a useful level of performance requires efficient use of the available optical gain and minimizing both the optical loss and heat generated in the surface emitting structure.
A partial solution to the gain problem is disclosed by S. W. Corzine, et al., in "Design of Fabry-Perot Surface-Emitting Lasers with a Periodic Gain Structure", IEEE Journal of Quantum Electronics Vol. 25(6), pp. 1513-1524, June 1989. Corzine teaches periodically spacing the active layers between the mirrors of the surface emitting laser cavity. The optimum spacing is chosen such that the active layer coincides with the maximum in the standing wave pattern of the optical field set up by the cavity mirrors. This spacing is approximately one-half of the lasing wavelength in the semiconductor.
Although such periodic gain enables more efficient use of the optical gain than a uniformly excited active layer, this approach has several limitations. For example, the threshold current increases as the bandgap of the passive layer between pairs of active layers is increased, thereby preventing the maximum confinement of charged carriers in the active layer, which is needed for operation at high temperatures. Furthermore, Corzine teaches placement of the periodic gain region within a laser cavity formed by two distributed Bragg reflectors, both of which require at least 18 to 25 layers to achieve the required level of reflectivity. Maximizing the electrical conductivity of these layers is not consistent with minimizing their optical absorption. Finally, Corzine fails to provide any means for electrically exciting the active layers.
Another problem for surface emitting lasers is that achieving a useful level of performance requires minimizing optical loss in the surface emitting structure. Consequently, using undoped active and passive layers throughout the construction of such lasers is desirable, in order to avoid optical absorption from free carriers. However, undoped layers have poor electrical conductivity, which is not consistent with the low electrical resistance required to minimize the heat generated in injection type diode lasers. This is especially a problem when the electrical current must pass through 20, 30 or more layers in the gain region and another 20 to 30 layers in each of the cavity mirrors. Excessive heating in the surface emitter not only increases the threshold current, but most seriously shifts the lasing wavelength away from the optimum wavelength of the cavity mirrors.
A partial solution to the optical loss/conductivity problem is disclosed by A. Scherer, et al., in "Fabrication of Low Threshold Voltage Microlasers", Electronics Letters Vol. 28(13), pp. 1224-1226, June 1992. In Scherer's approach, current is injected through a thin heavily doped contact layer grown under the output mirror of the cavity, thereby avoiding the current having to pass through one undoped mirror. However, the current must still pass through the other cavity mirror, which is highly doped for electrical conductivity and therefore introduces significant optical loss. The current must also pass through the active layers, which are undoped and are therefore electrically resistive. Therefore, it is impractical to combine the contacting approach of Scherer with the periodic gain teachings of Corzine. In addition, implementing Scherer's contact requires etching through the output mirror to expose the underlying contact layer, thereby introducing undesirable manufacturing cost and complexity, as well as potentially lowering the yield due to damage to the mirror.
Accordingly, there is need for designs and fabrication techniques which enable low current, low voltage and high temperature operation of surface emitting diode lasers. Beneficially, those designs and fabrication techniques should be applicable to constructing arrays of closely spaced, independently addressable surface emitting lasers.
3. Related Application
In U.S. Pat. No. 5,376,583 novel methods are disclosed for producing p-type wide bandgap material by impurity induced layer disordering (IILD) of multiple semiconductor layers and for simultaneously producing n-type and p-type IILD materials in the same set of multiple semiconductor layers.